Download Heat and Temperature

Heat and Temperature
Energy that makes things hot!
Outline
Review of Principle of Conservation of Energy.
Temperature and Thermal Equilibrium.
 Heat Capacity
 Thermal Expansion
 Temperature Measurements
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Conservation of Energy
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E total = Ek + EP
Energy conversions: The Faith Pendulum.
Hydroelectric Power
 EP
work turning a turbine.
Wind Power
 Ek
work turning the rotor blades.
Heat Power
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Work turning the fan
Thermal Equilibrium
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Hot chili and cold coke example
Definition:
 Heat is what flows between two objects when there is a difference in
temperature.
 Heat flows from the higher temperature to the lower temperature, so that the
higher temperature falls, and the lower temp. rises!
 Heat flows until the two temperatures are the same, and then it stops.
Heat and Temperature
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Heat = Q (units?)
Temperature = T (degrees C for now)
Heat Capacity = c:
 Q = c m ÄT
 “Heat” = “Heat Capacity” times “mass” times “change in Temperature”
 Answers the question: How much heat must I add to raise or lower the
temperature?
Heat Capacity demonstrations
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Heating a wax paper cup
Heating a wax paper cup with water
 Heating a balloon
 Heating a balloon with water
 Which cools off first? The aluminum pan or the cheese on the pizza?
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Heat Units
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A calorie: the amount of heat needed to raise 1 gram of water from 14.5 C to 15.5 C
 So, c = 1 cal/g-C
A Btu (British thermal unit): the amount of heat needed to raise 1 pound of water
from 63 to 64 F.
 Then c = 1 Btu/lb-F
A Food calorie is 1 kilocalorie or 1,000 calories.
Heat is energy!
1 calorie = 4.18 Joules; 1 Btu = 1055 Joules.
Heat Capacity examples
Heat capacity of water c = 1 cal/g-C; of gold, c = .03 cal/g-C.
How much heat is needed to raise the temperature of 100 g of water 10
C?
 Q = 1cal/g-C x 100 g x 10 C = 1,000 cal
 How much heat needs to be released to raise the temperature of 100g of
gold by 10 C?
 Q = .03cal/g-C x 100 g x 10 C = 30 cal
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Thermal Equilibrium
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Two objects at different temperatures are placed together.
By energy conservation – Q lost by the hotter one must equal Q gained by the
lower one.
The final temperature of the two objects will be the same.
The ratio of heat capacities (and masses) tells the relative temperature change.
 For equal masses of gold and water: c water / c gold = 1 / .03 = 33 --- gold will
change in temperature 33 times as much as the water.